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Passive Cooling Article in “The Bozone”

Greenovision had another article published! Check out “Passive Cooling Design: free home air conditioning!” on page 1A of the EcoZone section in the September 1st, 2014 Edition of the The BoZone. Greenovision homes are designed to be naturally warm in the winter and cool in the summer. In case you can’t read the article online, here it is reprinted below:

Passive Cooling Design: Free Home Air Conditioning!

By Mark Pelletier and Emily Varmecky

We recently had the pleasure of spending some time in a passive solar house that we designed and built a few years back. Although the home was designed to be heated by the sun’s radiant energy during the cooler months, the roof overhangs block out the sun during the summer. We were visiting on hot, sunny days in July, yet the interior of the home felt fresh, cool, and comfortable. It was great to experience firsthand how the home was benefiting from the passive cooling strategies that we had carefully implemented.

During the hot summer months, a passive air conditioning system is achieved through three strategies: cross ventilation, convection through stack effect, and Venturi effect. By utilizing a combination of these different passive strategies, a home can be cooled on both breezy and non-breezy days. In order to set up these effects within a home, windows are positioned low to the floor on the cool side of the building and high windows are positioned on the high-wall side of the building. Stack effect, for example, helps to cool the home on a non-breezy day. In this strategy, a natural vacuum is generated throughout the home when hot air rises and exhausts through the high windows and fresh, cool air enters through the low windows. The air pressure differences due to hot and cold variations inside the building and outside the home create a natural cross breeze. This air movement encourages evaporation of moisture on our skin and gives the sense of cooling. AKA, free air conditioning! Prevailing wind directions are also taken into effect to further pressurize the home, promoting a jet-like Venturi effect, which increases air flow rate within the home.

All three processes are passive; they require no special technological devices, just good design. That being said, to benefit from passive cooling in your own home, it is important to hire a home designer who is experienced in passive cooling design. Most conventional homes have flat 8 foot high ceilings without any height difference. In addition, the windows are typically all at the same height, which doesn’t allow for stack effect to set up convective air flow. Folks living in a conventional home find that to be relieved of the hot, stuffiness of their home, they must run electric fans and air conditioners all summer long. This can lead to an expensive energy bill.

We typically design homes with walls of different heights, which are often achieved through shed roofs. The width of the building, an open floor plan (fewer inner walls), and proper window heights/types are other critical aspects to consider when designing a home to be cooled passively.

Passive cooling strategies can help eliminate the need to run energy-consumptive air conditioners and fans, which lowers home energy bills. According to the Sonoran Institute, by 2026 Gallatin County could add as many as 26,000 new homes. As traditional fuel sources become more expensive, we hope to see more homes designed and built to be cooled passively.